A rifle is a type of weapon that fires rounds. Typically, the rifle includes a trigger, a hammer, and a barrel. The round is positioned in the barrel, and, when the trigger is pulled, the hammer fires the round through the barrel. A modular rifle typically includes a lower receiver assembly, an upper receiver assembly housing the barrel, and a coupling mechanism. The M-16 style rifle is a type of modular rifle system commonly used by military and police forces that features a gas-operated bolt and bolt carrier system, as disclosed, for example, in U.S. Pat. No. 2,951,424, issued to Eugene M. Stoner on Sep. 6, 1960 (incorporated herein by reference in its entirety). The AR-15 style rifle is a similarly designed modular rifle system commonly sold and used in civilian applications.
For most M-16/AR-15 style rifle systems, the upper receiver is fashioned out of forged lightweight aluminum on account of its machinability and corrosion resistance. While machining the upper receiver from a solid billet of aluminum may offer added strength over forging of the receiver, the aluminum material of the upper receiver is nevertheless subject to degradation and deformation to the high gas temperatures and operation of the bolt carrier system inside the upper receiver. The bolt carrier is typically fashioned out of hardened steel or another material with similarly higher heat and wear tolerances than aluminum. Friction created by repeated operation of a steel bolt carrier system within an aluminum upper receiver usually causes material wear and shortens the life cycle of the aluminum upper receiver and rifle system.
Providing a system and method for allowing the internal upper receiver assembly to be strengthened with a hardened steel or other high-strength-material liner inside which the bolt carrier system operates provides for a strengthened upper receiver assembly, such that the upper receiver and barrel provide a continuous chamber consisting of high-heat-tolerant and wear resistant material in which the bolt carrier system operates. This leads to increased reliability and longevity of the upper receiver and the life cycle of the rifle system.